JP-A-2000-238515 describes a wheel-state obtaining apparatus, which includes wheel-side devices respectively provided on a plurality of wheels of a vehicle, and a body-side device disposed on a body of the vehicle, and wherein wheel-side information is transmitted from the wheel-side devices to the body-side device, so that information indicative of the states of the wheels is obtained. Each of the wheel-side devices includes an air-pressure detecting device operable to detect an air pressure of a tire of the corresponding wheel, and a transmitter device operable to transmit information indicative or representative of the air pressure detected by the air-pressure detecting device, while the body-side device includes a receiver device operable to receive the information transmitted from the wheel-side devices, and an air-pressure-information obtaining device operable to extract the information representative of the air pressure, from the wheel-side information received from the wheel-side devices. Each wheel-side device is arranged to transmit the wheel-side information at a predetermined first time interval while the detected tire air pressure is changing at a relatively low rate, and at a predetermined second time interval shorter than the first time interval, while the tire air pressure is changing at a relatively high rate. Accordingly, the body-side device receives the wheel-side information at the first time interval while the tire air pressure of each wheel is changing at the relatively low rate, and at the second time interval while the tire air pressure of the wheel is changing at the relatively high rate.
In the wheel-state obtaining apparatus described above, the wheel-side information including the information representative or indicative of the air pressure is transmitted from each wheel-side device, and the transmitted information is received by the body-side device, and the information representative of the air pressure is extracted from the received wheel-side information. Where the body-side device cannot receive the wheel-side information due to a noise, for example, the wheel-state obtaining apparatus cannot obtain the air pressure information.